If you think this is bad, then you should make sure to use copyleft licenses.
EDIT: Just read the details, and it seems that this is just what they did. SSPL is like AGPL with a stronger SAAS is distribution claus. That might not be valid, according to the OpenSource definition, but unless you are planning to modify the code and provide it as SAAS I think this is no a problem.
Didn't they switch to a license with stronger mechanisms to keep the source available? SSPL, is basically AGPL but have even stronger protection from large corperations to use the code in their data centers without contributing the changes back. This is basically a move to prevent AWS/Google/Microsoft/et al, from leaching on the contributors work without giving anything back.
Or am I reading this wrong?
EDIT: Note, that the Mastodon account is to an AWS employee.... so for him, this might be bad, since it no longer allows them to have their own internal fork without contributing back. Now, they will need to use a real for and maintain that them selves without leaching on the redis contributors.